docs: def what(self):
          """
          May return a 'postponed' or 'rescheduled' string depending what
          the start and finish time of the event has been changed to.
          """
          originalFromDt = dt.datetime.combine(self.except_date,
                                               timeFrom(self.overrides.time_from))
          changedFromDt = dt.datetime.combine(self.date, timeFrom(self.time_from))
          originalDaysDelta = dt.timedelta(days=self.overrides.num_days - 1)
          originalToDt = getAwareDatetime(self.except_date + originalDaysDelta,
                                          self.overrides.time_to, self.tz)
          changedDaysDelta = dt.timedelta(days=self.num_days - 1)
          changedToDt = getAwareDatetime(self.except_date + changedDaysDelta,
                                          self.time_to, self.tz)
          if originalFromDt < changedFromDt:
              return _("Postponed")
          elif originalFromDt > changedFromDt or originalToDt != changedToDt:
              return _("Rescheduled")
          else:
              return None